The broad use of portable host computers, including Personal Digital Assistants (PDAs), has been severely hampered by limited capabilities for expansion or customization. Expansion and application customization has been performed via only one, or at most two, slots for removable expansion cards for I/O, I/O adapters, memories, and memory adapters. Memory expansion cards have included DRAM, SRAM, ROM, and Flash technologies. I/O expansion cards have included dedicated peripherals, networking, modems, wireless communications, serial I/O, and bar-code and other scanners.
Having only one slot meant choosing between memory or peripheral expansion. In two-slot implementations, one of the slots is generally used for peripheral expansion, and the other for memory expansion. As market forces and consumer demand are pushing future PDAs to be ever smaller, allocating packaging volume for two-slots will be increasingly viewed as a costly and nonviable solution.
Memory and Expansion Card Standards
Two of the most popular industry standards for the slots and removable cards are the PC Card and the CompactFlash Card. The PC Card has a 16-bit variant, previously known as a PCMCIA card, and a newer 32-bit variant, also known as a Card-Bus card. U.S. Pat. No. 5,815,426 ('426), ADAPTER FOR INTERFACING AN INSERTABLE/REMOVABLE DIGITAL MEMORY APPARATUS TO A HOST DATA PART, assigned to Nexcom Technology, and hereby incorporated by reference, describes these and other removable expansion card and memory types suitable for PDAs. In addition to the PC Card and CompactFlash Card formats, the '426 patent includes discussions of and references to Miniature Cards, Sold State Floppy Disk Cards (SSFDCs), MultiMediaCards (MMC), Integrated Circuit (IC) Cards (also known as Smart Cards), and Subscriber Identification Module (SIM) Cards.
CompactFlash Card
FIGS. 1A, 1B, and 1C are different views of a prior art Type II CompactFlash Card. The CompactFlash physical, electrical, and software interface architecture is taught in the CompactFlash Specification Revision 1.3, Copyright 1998, by the CompactFlash Association, P.O. Box 51537, Palo Alto, Calif. 94303, which is hereby incorporated by reference. FIGS. 1A, 1B, 1C, part of 6A, and part of 6B are reproduced or derived from the CompactFlash Specification document.
U.S. Pat. No. 5,887,145 ('145), REMOVABLE MOTHER/DAUGHTER PERIPHERAL CARD, assigned to SanDisk Corporation, and hereby incorporated by reference, describes the required features of host systems for CompactFlash Cards, including controllers required by CompactFlash memory cards (CF cards) and comprehensive controllers required by CompactFlash memory and I/O cards (CF+ cards).
MultiMediaCard
FIGS. 2A and 2B represent a prior art MultiMediaCard form factor and its pad definitions. FIGS. 3A and 3B represent the prior art internal architecture of a generic MultiMediaCard and its registers. FIG. 4A illustrates the prior art functional partitioning of a generic MultiMediaCard system. FIG. 5 illustrates the prior art physical partitioning of a generic MultiMediaCard system.
The MMC and MMC related system issues are taught in the MultiMediaCard System Summary Version 2.0, Copyright January 1999, by the MultiMediaCard Association, 19672 Stevens Creek Blvd., #404, Cupertino, Calif. 95014-2465, which is hereby incorporated by reference. FIGS. 2A, 2B, 3A, 3B, 4, 5, and part of 6A are reproduced or derived from the MultiMediaCard System Summary document.
FIGS. 6A and 6B are different views comparing the form factors of the prior art CompactFlash Card (top) and MultiMediaCard (bottom). In each of 6A and 6B, the CompactFlash Card and the MultiMediaCard are both roughly to equal scale.
Adapters for Removable Memories
Adapters exist or have been prophetically disclosed for physically and electrically coupling a removable memory on a slide, or stick, to a portable host via a removable expansion card of either the PCMCIA Card or CompactFlash Card form factors. The previously mentioned '426 patent describes such removable memory adapters. The focus of these existing memory adapters has been limited to merely providing an interface adapter, or bridge, between a first interface type (the host to removable-expansion-card interface) and a second interface type (the removable memory stick).
PC Card Mother and CompactFlash Card Daughter Combinations
Adapters exist or have been prophetically disclosed that comprise a special mother PC Card designed to accept one or more daughter CompactFlash Cards of one or more types. The previously '145 patent describes such CompactFlash adapters. The focus of these existing mother/daughter combinations has also been limited. First, the daughters have been used for memory expansion for the host platform, primarily in the form of flash-memory-based mass-storage-like devices. In this first approach, the mother card provides the requisite mass-storage controller functionality. Second, the daughters have been used for dedicated peripheral, I/O, or communication functions. In this second approach, the mother card has a so-called comprehensive controller that augments the mass-storage controller functionality with functions commonly required or useful to multiple daughter cards. Third, in a variation of either of the first two paradigms, functions of the general-purpose host may be relocated to the mother card.
Background for PC-Card Based I/O Functions
Techniques are known in the art for making and using systems that perform such I/O functions in a PC card. For example, see U.S. Pat. No. 5,671,374 ('374), PCMCIA INTERFACE CARD COUPLING INPUT DEVICES SUCH AS BARCODE SCANNING ENGINES TO PERSONAL DIGITAL ASSISTANTS AND PALMTOP COMPUTERS, assigned to TPS Electronics, which is hereby incorporated by reference. The '374 patent teaches the use of PDAs and similar hosts equipped with PC card interfaces for I/O devices including portable laser-scanners, magnetic stripe and ink readers, keyboards and keypads, OCR devices, and trackballs.
Techniques are also known in the art for making and using PC Card-based radios for applications based in a portable host. For example, see U.S. Pat. No. 5,519,577 ('577), SPREAD SPECTRUM RADIO INCORPORATED IN A PCMCIA TYPE II CARD HOLDER, assigned to Symbol Technologies, and hereby incorporated by reference.
Techniques are also known in the art for making and using disk emulation devices based on flash memory. For example, see U.S. Pat. No. 5,291,584 ('584), METHODS AND APPARATUS FOR HARD DISK EMULATION, assigned to Nexcom Technology, and hereby incorporated by reference.
Background for Relevant Application Specific Functions
Techniques are known in the art for making and using systems that download or capture compressed digital audio for storage and later playback using dedicated removable media. For example, U.S. Pat. No. 5,676,734 ('734), SYSTEM FOR TRANSMITTING DESIRED DIGITAL VIDEO OR AUDIO SIGNALS, assigned to Parsec Sight/Sound, and hereby incorporated by reference, teaches a system for transmitting digital video or audio signals over a telecommunications link from a first to a second party. In addition, U.S. Pat. No. 5,579,430 ('430), DIGITAL ENCODING PROCESS, assigned to Fraunhofer Gesellschaft zur Foerderung der angewandten Forschung e.V., and hereby incorporated by reference, teaches processes for encoding digitized analog signals. Such processes are useful for insuring high-quality reproduction while reducing transmission bandwidth and data storage requirements.
Techniques are also known in the art for making and using record and playback portable host devices based on a dedicated flash memory. For example, see U.S. Pat. No. 5,491,774 ('774), HANDHELD RECORD AND PLAYBACK DEVICE WITH FLASH MEMORY, assigned to Comp General Corporation, and hereby incorporated by reference, and U.S. Pat. No. 5,839,108 ('108), FLASH MEMORY FILE SYSTEM IN A HANDHELD RECORD AND PLAYBACK DEVICE, assigned to Norris Communications, also hereby incorporated by reference.
Limitations of Previous Approaches
In general purpose portable hosts, populating an expansion slot has meant choosing one of either removable memory or peripheral expansion for that slot. When used for memory expansion, the removable memory has been limited to use for the system or application software running on the host. In essence, the removable memory has only been used as host-dedicated memory. This was done either directly, e.g., as some portion of the main-memory of the host, or indirectly as an emulation substitute for host mass-storage (i.e., disk drives).
When used for I/O expansion, the expansion I/O-cards have not had access to a private removable media/memory. This has prevented portable computer hosts, such as PDAs, from being used as a customizable platform for many application-specific functions that require a removable memory dedicated to the application.